Robotics End effector and its basic type.pdf
- 1. Robot end effector Defination an end-effector is a device that attached to the wrist of the robot arm and enable the general purpose robot to perform specific task. Types of End effector 1. Gripper 2. Tools
- 2. Gripper Gripper are the end effector used to grasp and hold objects The objects are generally workparts that are to be moved by robot. Types of Gripper 1. Mechanical Gripper 2.Vaccume cup 3.Magnetive gripper
- 3. Mechanical Gripper Mechanical gripper is an end effector that uses mechanical fingers actuated by mechanism to grasp an object. The fingers are sometimes called jaws,which are appendages of gripper that actually make contact with the object. The fingers are either attached to mechanism or are an integral part of mechanism. If the fingers are of attachable type, then they can be detached and replaced. The used of replaceble fingers wear and fingers allows for interchangibility
- 4. Different set of finger for used with same gripper mechanism can be designed to accomodate different part model an example of interchangability feature is illustrate in fig in which gripper are designed to accomodate fingers of varying size
- 5. The function of gripper mechanism is to translate some form of power input into grasping action of finger against the part . the power input is supplied from the robot and can be Pneumatic, electric or hydrolic. The Mechanism must be able to open or close the finger.
- 6. Mechanical gripper are also classified according to the type of kinematic device used to actuate the finger movement. 1.Linkage actuation. 2.Gear and Rack actuation 3.Cam actuation 4.Screw Actuation 5.Rope and Pulley actuation 6.Miscellaneous.
- 7. Linkage Actuation The linkage category covers a wide range of design posibilities to actuate the opening and closing of gripper. The design of linkage determine how the input force Fa to the gripper is converted to Gripping force Fg applied by the fingers
- 8. Gear and Rack Actuation Fig. illustrate the one method of actuating the gripper fingers using a gear and rack configuration. The rack gear would be attached to a piston or some other mechanism that would provide a linear motion. Movement of rack would drive two partial pinion gear and these would in turn open and close the fingers.
- 9. Cam Actuation The cam actuated gripper include a variety of possible design,one of which is shown in fig. a cam and follower arrangement , often using a spring loaded follower can provide the opening and closing of gripper. Movement of cam in one direction would force the gripper to open, while the movement of cam in opposite direction would cause the spring to force the gripper to close.
- 10. Screw type actuation Method Screw type actuation method is shown in fig. the screw is turned by motor, usually acompanied by speed reduction mechanism. When the screw is rotated in one direction, this cause a threaded block to be translated in one direction.when the screw is rotated in opposite direction, the threded block is rotated in opposite direction. The threded block is in turn connected to gripper fingersto cause the corrosponding opening and closing action.
- 11. Rope and pulley Mechanism Rope and pulley mechanism can be designed to open and close a mechanical gripper. Because of Nature of these mechanism, some form of tension device must be used to oppose the motion of the rope in the pulley system. the pulley system might operate in one direction to open the gripper, and the tension device would take up the slack in the rope and close the gripper when pulley system operate in opposite direction.
- 12. Miscellaneous Actuation The miscellaneous category is included in our list to allow for gripper actuating mechanism which do not logicaly fall in to above category an expandable bladder or diaphragm that would be inflated and deflated to actuate the gripper finger.
- 13. Other types of gripper Other type of gripper are the following 1.Vaccum cup 2.Magnetic Gripper 3.Adhesive gripper 4. Hook,Scoop and other Miscellaneous gripper etc
- 14. Vaccum cup Vaccum cup also called suction cup,can be used as gripper device for handling certain type of object.the usual requirements on the object to be handled are that they be flat, smooth and clean,condition necessary to form a satisfactory vaccum between object and suction cup Vaccume pump is piston operated or vane driven device powered by an electric motor. It is capable of creating relatively high vaccum Ventury is simpler device as pictured in fig and can be driven by means of shop air pressure its initial cost is less than that of vaccum pump
- 15. The overall reliability of the vaccume system is dependant on source of air pressure the lift capacity of suction cup depend on effective area of cup and negative air pressure between the cup and the object. the relation can be summerized as following equation. F=PA where F-force or lift capacity, lb P- Negative Pressure and A- total effective area of suction cup used to create vaccum.
- 16. Effective area of cup during operation is approximately equal to the uniform area determined by diameter of suction cup. the squashing action of cup as it presses against the object would tend to make the effective area slightly larger than uniform area on the othr hand,if centre portion of cup makes contact against the object during deformation, this would raduce the effective area over which vaccum is applied.these two condition cancel each other out.
- 17. Negative air pressure is pressure differential between the inside and outside of vaccum cup.
- 18. Magnetic Gripper Magnetic gripper can be very feasible means of handling ferrous material Magnetic gripper offers the following avantages in robotic handling appication 1.Pick up time are very fast 2. Variation part size can be tolerated. gripper does not have to be designed for one perticular workpart. 3. they have the ability to handle meta parts with holes (not possible with vaccum gripper) 4. they require only one surface for gripping.
- 19. Dis advantage 1. with magnetic gripper include the residual magnetism remaining in workpiece which may cause problem in subsequant handling and the possible side slipage and other errors which limit the precision of this means of handling. 2. Another disadvantage of a magnetic gripper is the problem of picking up only one sheet from a stack.
- 20. Magnetic gripper can be divided in two Categorise 1.Using electromagnet 2. Using Permanant Magnet Electromagnetic Gripper - Electromagnetic gripper are easier to control, but require a source of DC power and an appropriate controller unit. when part is to be released the controller unit reverses the polarity at a reduced poer level before switching of the electromagnet. this procedure act to cancel residual magnetism in the workpiece and ensure positive release of parts.
- 21. By using permanant Magnet Permanant magnet have advantage of not requiring an external power source to operate the magnet. However, there is loss of control that acompanies this apparent advantage When part is to be released at the end of handling cycle, some means of separating the part from the magnet must be provided.the device which accomplished this is called a stripper or stripping device. its function is to mechanically detach the part from magnet. one possible stripper design is shown in fig.
- 22. Adhesive Gripper Gripper design in which an adhesive substance perform the grasping action can be used to handle fabrics and other lightweight material. one of the potential limitation of an adhesive gripper is that the adhesive loses its tackiness on repeated uses. conseqently its reliability as gripping device is diminished with each succesive operation cyle. to overcome this limitation, the adhesive material is loaded in the form of contineous ribbon into feeding mechanism that is attached to robot wrist. feeding mechanism operate in a mannersimilar to a typewriter ribbon mechanism.
- 23. Hooks, Scoops and other Miscellaneous Devices Hooks can be sed as end effector to hande container of parts and to load and unload parts hanging from overhead conveyor the item to be handled by a hook must have some sort of handle to enablethe hook to hold it.
- 24. Scoop Scoops and ladles can be used to handle certain material in liquid or powder form. Chemical in liquid or powder form, food materials, grannular substance and molten metals are all example of material that can be handled by robot using this method of holding one of its limitation is that the amont of material being scooped by robot is sometimes difficut to control. sprillage during handling cycle is also a probem.
- 25. Other type of Gripper Other type of gripper incude inflatable device, in which an inflatable bladder or diaphragm is expanded to grasp the object. The inflatable bladder is fabricated out of rubber or other elastic material which makes it appropriate for gripping fragile object. gripper applies a uniform grasping pressure against the surface of the object rather than a concentrated force typical of mechanical gripper. an example of inflatable bladder type gripper is shown in fig part a of fig shows bladder fully expanded, part b shows bladder used to grasp the inside diameter of bottle.
- 26. Tools as end effector In Many application, robot is required to manipulate a tool rather than a workpart. the end effector is a gripper that is designed to grasp and handle the tools. the use of gripper permits the tools to be exchanged during the cycle and thus fascillates this multitool handling function. In most of the robot application in which a tool is manipulated, the tool is directly attached to the robot wrist. in these cases tool is end effector some example of tools used as end effector in robot application include 1. spot welding tools 2. Arc Welding Torch
- 27. 3. spary painting nozzle 4. Rotating spindle for operation such as a. Drilling b. routing c. wire brushing d. grinding 5. Heating Torches 6. Water jet cutting tools. In each case, the robot must contol the actuation of the tool.